Attribute groups during registration

Hello,

I think I have read about this on the forum but I can't find the topic corresponding. So here's my question :
How can we do to attribute group during registration ? By example, a student suscribes and chooses his subject like "spanish".
I would like it automatically makes him part of the Joomla's Group's users " Spanish".

I know this feature isn't currently implemented but I remember I have read on this forum that's is possible by customising with php. Can I have a clue about this ?
Secondly, would this feature be implemented soon ?

Thanks a lot,

EG